Get out Rick, a growing Republican chorus says. Forget it, responds Rick Santorum to the calls to drop his increasingly long-shot bid for the GOP presidential nomination.

The pressure to withdraw is actually incentive for Santorum to stay in the race.

It keeps the media spotlight on him and bolsters the image he constantly projects of himself as the lone conservative battling the GOP establishment's desire for the more moderate Mitt Romney to face President Barack Obama in November.

Both elements are vital to the former U.S. senator from Pennsylvania, who has seen his campaign rise from shoestring status to become the main conservative challenge to Romney's front-running bid.

While primary results and the delegate count work against him, Santorum can exploit his underdog status by continuing to hammer themes at the heart of his campaign -- that only a true conservative can beat Obama and that Romney lacks conservative principles valued by tea party supporters and Christian evangelicals who make up Santorum's base.

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"The more the establishment tries to force (Santorum) out of the race, the stronger his argument is with the grass-roots that the establishment is ganging up on him and being unfair," said Darrell West, vice president and director of governance studies at the Brookings Institution. "He can play to voter suspicions that national leaders don't have their best interests at heart."

Romney's recent run of primary victories, including the three held Tuesday in Wisconsin, Maryland and Washington, D.C., prompted more declarations from Republicans that the race was over.

Veteran Sen. John McCain, the GOP presidential nominee who lost to Obama in 2008 and backs Romney this year, said Wednesday that "whether Rick Santorum stays in or not, is now basically irrelevant."

Romney has "a lot of ground to make up," and "every day that goes by that he's not in the general campaign is a day lost," he said.

Santorum has made light of the growing calls to get out, trying to turn the issue to his advantage.

"I think I've enjoyed about eight months of people saying that," he said Wednesday while campaigning in Pennsylvania. "Everyone has been asking me, from the days I was traveling around in the truck in Iowa, to get out of the race. I've never been the party establishment's candidate. And that holds true to today."

On Thursday, Santorum met with conservative leaders in person and by telephone to discuss a way forward against Romney, including trying to woo supporters from fellow challenger Newt Gingrich, according to sources familiar with the talks.

A Santorum campaign statement obtained by CNN later Thursday challenged media tallies of the delegate count so far and said the race was much closer than portrayed.

In addition, the statement said Santorum's campaign was working with Gingrich's campaign on how to prevent Romney from reaching the 1,144 delegates needed to clinch the nomination before the Republican convention in August.

Santorum is the first to point out Romney's huge advantage in money and organization in the campaign, noting how the former Massachusetts governor and his supporting super PAC have greatly outspent him. At the same time, Santorum's campaign has demonstrated repeated inadequacies, such as failing to make the ballot in Virginia or qualify delegates in parts of some other states.

When asked about such problems, Santorum has focused on the successes of such a bare-bones campaign, again depicting himself as the conservative David against Romney's establishment Goliath. It is part of his efforts to contrast his own blue-collar roots with Romney's personal wealth and Wall Street background.

"You're looking at someone who, you know, knows this area -- knows Pennsylvania better than, certainly anybody in this race," Santorum said Wednesday. "Someone who has ... the values forged from the values here in Southwestern Pennsylvania."

The candidate continued: "And I think that, when you look at where -- the contrast that we can provide in this election -- that someone from a blue-collar, working-class town in Butler, Pennsylvania, grew up in government housing and who, you know, clawed his way ... through the political process, never being anybody's favorite, always being the underdog, always being someone that was discounted. And I think folks in Pennsylvania have, for a long time, admired that story and can relate to that story. And I think they will again in this election."

Santorum is basing his campaign's future on winning Pennsylvania when the Keystone State holds its primary on April 24. He said Wednesday that the month of May includes primaries in several states more favorable to his conservative message, including Texas on May 29.

"May looks very, very good," Santorum told reporters, musing about the possibility of Texas making its 154 delegates winner-take-all. However, a Texas election official told CNN that the delegates will be allocated on a proportional basis and that can change only through a series of steps involving local, state and national Republican bodies.

Polls in Pennsylvania indicate that Santorum holds a dwindling lead over Romney, who is campaigning hard in the state to try to undermine any rationale for Santorum's continued candidacy.

"Pennsylvania's going to be extremely important," Republican National Committee Chairman Reince Preibus said on Wednesday. "I think these candidates, for whatever it's worth, have set up a narrative that if you can't win your home state, that spells a pretty big problem."

Santorum's campaign communications director, Hogan Gidley, said Wednesday that a drop in the polls before the Pennsylvania vote would have no impact on Santorum's plans.

"It's not about wins and losses for Rick Santorum. It's about fighting for freedom," Gidley said. "This campaign is not poll driven."

To West, the Brookings Institution analyst, Santorum's continued candidacy amounts to a "no-lose proposition" for now because he "continues to make his argument and solidify his standing among the grass-roots."

"As long as you have a platform and you're running a low-budget campaign, there's no need to get out of the race," West said. "You're not facing big debts from staying in, and you can potentially help yourself for the next time around."

Santorum has hinted at a "next time around," pointing out this week that his situation now is similar to that of another conservative: Ronald Reagan, who faced calls to drop out of the race in 1976.

Reagan did not, and while he failed to win the nomination at the Republican convention that year against incumbent President Gerald Ford, the campaign positioned the former California governor for his successful run in 1980.

Santorum said that Republicans should nominate him now instead of repeating the mistake of 1976 by going with the moderate Ford, who lost to Jimmy Carter, but West said Santorum's underlying strategy for staying in the race appears aimed at 2016 as much as 2012.

"Santorum does not appear concerned about hurting Romney," West said, noting that Santorum ran "very tough ads" in Wisconsin against Romney.

"If he weakens Romney and Romney loses the general election, Santorum benefits in 2016 because he can say, 'I told you so,' " West said. "That clearly is his strategy, because otherwise he would soften his rhetoric and drop out of the race."